The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, a conventional vehicle employs a siamese-type cylinder block in a multi-cylinder engine that is short in distance (bore pitch) between cylinders for the purpose of the reduction of the size, weight and entire length of the multi-cylinder engine. The siamese-type cylinder block is configured to be short in bore pitch since it has no water jacket (a cooling water passage) between cylinder liners and is formed by casting several cylinder liners using aluminum so as to combine them with each other.
Since the siamese-type cylinder block has a short distance in a portion (referred to as a siamese portion hereinbelow) between cylinder bores, it does not include the cooling water passage and thus is vulnerable to heat. Particularly, the siamese portion around an upper end part of the cylinder block to which heat from a combustion chamber is directly applied may become significantly high in temperature.
We have discovered that the high temperature that the siamese portion reaches causes a temperature difference between the siamese portion and a circumference thereof. Accordingly, an upper part of the cylinder block is thermally transformed greatly, and an epicenter of the cylinder bore is displaced. Further, engine oil may flow into a combustion chamber through a clearance occurring between a piston ring and an inner wall of a cylinder, which causes excessive consumption of the engine oil, and increases the amount of blow-by gas.
In the related art, to properly cool the siamese portion, slits or drilled holes formed in a portion between the cylinder bores, or wedge-shaped water holes formed through a cylinder head gasket that serve as a cooling water passage have been provided, but we have found that cooling efficiency thereof was low.
Particularly, in the related art, the following structures have been used: an insertion-type structure that improves a performance of an internal combustion engine by reducing an initial temperature of intake air by promoting a flow of cooling water in an upper part of an exhaust system of the cylinder block; and an insertion-type structure that divides a flow of cooling water into an upper flow and a lower flow for split cooling. However, the former structure is cast using a plastic, and due to a clearance for corresponding to a casting tolerance, the flow of the cooling water is distributed, which reduces cooling efficiency, whereas the latter structure requires an additional split cooling valve when applying an integrated flow control valve, which complicates the structure of an integrated valve and increases a size thereof.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.